This invention relates to a rechargeable storage cell of the type which employs a gas as one member and a chemically active solid state material as the other member of the electrochemical couple, and more particularly to a low pressure nickel hydrogen battery system.
Considerable attention has been devoted in recent years to development of electric vehicles. One deterrent is the high weight-to-energy storage ratio of the lead-acid battery. Among other things, this severely limits the cruising range between charges for such vehicles.
Substantial attention has been devoted to the development of electric power secondary cells which employ a gas as one member and a chemically active solid state material as the other member of the electrochemical couple. One such type is a cell in which the anode is a chemically oxidizable metal and the depolarizer is oxygen, e.g. zinc/air and cadmium/air batteries. A second type utilizes an electrochemically reducible metal oxide, e.g. nickel oxide, at the cathode and a gas that is oxidizable and ionizable, e.g. hydrogen, at the anode. A cell of the latter type is disclosed in U.S. Pat. No. 3,544,375 to S. Ruben for Rechargeable Fuel Cell, which requires feeding hydrogen gas into the cell when it is being discharged, venting hydrogen gas when the cell is being recharged and submerging the cathode and anode in the electrolyte. The hydrogen is claimed to be supplied under pressure, but the magnitude is not mentioned.
Dunlop et al. in U.S. Pat. No. 3,867,199 teaches as disadvantages to be avoided the requirements set forth by Ruben of feeding and venting hydrogen gas and of submerging the electrodes in the electrolyte, and instead proposes a high-pressure, hermetically sealed cell to prevent inflow and outflow of gas during charging and discharging. See also Tsenter et al. U.S. Pat. No. 3,669,744 and Holleck U.S. Pat. No. 4,127,703 for high pressure hermetically sealed cells. The charge and discharge conditions, cell constructions and operating data are described in an article by Giner and Dunlop, "The Sealed Nickel-Hydrogen Secondary Cells", Journal of the Electrochemical Society, Volume 122, number 1, pages 1-11 (January 1975). That article and the above mentioned U.S. patents are incorporated herein by reference.
The current state of the art relating to nickel hydrogen batteries is definitely that of high-pressure hermetically sealed cells. There are several problems associated with such cells. These include (1) expensive cell fabrication, (2) high self-discharge rates and (3) poor heat transfer characteristics. The application of nickel-hydrogen battery technology has therefore been limited to applications such as used in satellites. I am not aware of any current teaching or use of a cell as disclosed by Ruben, or any other low pressure nickel-hydrogen cell.